Dear Scott, Thank you for your advice. Q) I assume that your second solution allow different S02 values for each spectrum? I'd like to be more specific about my obtained results, At reference state (that means without any applied current), the amplitude reduction factor was 0.77At 20% charge, it was 0.6740% charge = 0.6660% charge = 0.6380% charge = 0.68full charge = 0.67 Most of the fitting parameters were reasonable and the result well corroborates with previous study (papers) from other group (but I'm not sure about the value of the amplitude reduction factor as there were little information about it). Kind Regards,HOON From: scalvin@sarahlawrence.edu To: ifeffit@millenia.cars.aps.anl.gov Date: Thu, 18 Sep 2014 07:23:53 -0400 Subject: Re: [Ifeffit] Inconsistency of the amplitude reduction factor Hi Hoon, Using a reference value is not always a good idea, because experimental effects can play a role. BUT, S02 should not change during charge-discharge on a single sample, or a series of samples prepared and measured similarly. Instead, it's likely something correlated with S02 in the fit is changing, and so the fitting routine is getting a bit confused and attributing part of the change to S02. (That's not a knock on the fitting routine; it doesn't know any better unless you tell it!) I think the best recommendation is to do a simultaneous fit on multiple spectra, constraining the S02 to be the same for each. So you're still fitting S02, but forcing all the spectra to use the same value. Second best is to fit one spectrum and allow S02 to vary, and then constrain all the other fits to use that value. --Scott CalvinSarah Lawrence College On Sep 18, 2014, at 7:06 AM, HOON Kim wrote:Hello, I am a bit confused about the amplitude reduction factor (S0^2), in a sense that whether this factor must be determined by fitting or constrained by a reference value for a specific element. I'm dealing with a cathode composite (for lithium-ion battery) comprised of two crystal phases. During charge-discharge, the amplitude reduction factor changes and at a certain state of charge (SOC) it changes a lot such as from 0.77 to 0.67. My understanding is that it may reflect the phase transition of the material into the amplitude reduction factor. But, I'm not sure ... I need advice on this. Thank you ! Kind Regards,HOON_______ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

By the way, you should also look closely at how well the edge jump is being determined by Athena (or whatever software you use for the data reduction). If there's a white line or pre-edge feature that's changing, it's possible the default behavior of Athena is not determining the edge jump in a consistent manner. That would directly lead to an apparent change in S02. The solution in that case is to adjust the parameters in Athena to assure the edge jump is determined in a consistent fashion. --Scott Calvin Sarah Lawrence College On Sep 18, 2014, at 8:20 AM, HOON Kim mailto:science@live.co.kr> wrote: Dear Scott, Thank you for your advice. Q) I assume that your second solution allow different S02 values for each spectrum? I'd like to be more specific about my obtained results, At reference state (that means without any applied current), the amplitude reduction factor was 0.77 At 20% charge, it was 0.67 40% charge = 0.66 60% charge = 0.63 80% charge = 0.68 full charge = 0.67 Most of the fitting parameters were reasonable and the result well corroborates with previous study (papers) from other group (but I'm not sure about the value of the amplitude reduction factor as there were little information about it). Kind Regards, HOON ________________________________ From: scalvin@sarahlawrence.edumailto:scalvin@sarahlawrence.edu To: ifeffit@millenia.cars.aps.anl.govmailto:ifeffit@millenia.cars.aps.anl.gov Date: Thu, 18 Sep 2014 07:23:53 -0400 Subject: Re: [Ifeffit] Inconsistency of the amplitude reduction factor Hi Hoon, Using a reference value is not always a good idea, because experimental effects can play a role. BUT, S02 should not change during charge-discharge on a single sample, or a series of samples prepared and measured similarly. Instead, it's likely something correlated with S02 in the fit is changing, and so the fitting routine is getting a bit confused and attributing part of the change to S02. (That's not a knock on the fitting routine; it doesn't know any better unless you tell it!) I think the best recommendation is to do a simultaneous fit on multiple spectra, constraining the S02 to be the same for each. So you're still fitting S02, but forcing all the spectra to use the same value. Second best is to fit one spectrum and allow S02 to vary, and then constrain all the other fits to use that value. --Scott Calvin Sarah Lawrence College On Sep 18, 2014, at 7:06 AM, HOON Kim mailto:science@live.co.kr> wrote: Hello, I am a bit confused about the amplitude reduction factor (S0^2), in a sense that whether this factor must be determined by fitting or constrained by a reference value for a specific element. I'm dealing with a cathode composite (for lithium-ion battery) comprised of two crystal phases. During charge-discharge, the amplitude reduction factor changes and at a certain state of charge (SOC) it changes a lot such as from 0.77 to 0.67. My understanding is that it may reflect the phase transition of the material into the amplitude reduction factor. But, I'm not sure ... I need advice on this. Thank you ! Kind Regards, HOON _______ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.govmailto:Ifeffit@millenia.cars.aps.anl.govhttp://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.govmailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

On 09/18/2014 08:20 AM, HOON Kim wrote:

I'd like to be more specific about my obtained results,

At reference state (that means without any applied current), the amplitude reduction factor was 0.77 At 20% charge, it was 0.67 40% charge = 0.66 60% charge = 0.63 80% charge = 0.68 full charge = 0.67

My other comment on this thread is that you are not being specific enough. Without error bars, it is not possible to interpret those numbers in any physically meaningful way. Similarly, without knowing the uncertainty, it is hard for us to comment substantively on your question. I would imagine that, given the likely size of your error bars, 0.63 and 0.68 are not different results. In fact, it is possible that 0.63 and 0.77 are not different in any defensible way. That may be yet more likely given the possibility of systematic error due to changes in morphology -- which would not be properly captured in the statistical error bars -- as I mentioned in my last post. Remember: ALWAYS cite error bars with numbers from a fit! B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/

On 09/18/2014 07:23 AM, Scott Calvin wrote:

Hi Hoon,

Using a reference value is not always a good idea, because experimental effects can play a role.

I want to elaborate a bit on this point in Scott's post, particularly given the nature of your sample. The materials in a battery, as they charge or discharge, can undergo changes in morphology. Morphology can have an impact on the measured amplitude. More specifically, inhomogeneity in the sample -- pinholes, for instance -- have a known effect on the amplitude. See, for example: http://dx.doi.org/10.1103/PhysRevB.23.3781 http://dx.doi.org/10.1016/0167-5087(83)90730-5 http://gbxafs.iit.edu/training/thickness_effects.pdf My point is that you may need to question the assumption that S02 even should be transferable in your measurement. B

BUT, S02 should not change during charge-discharge on a single sample, or a series of samples prepared and measured similarly. Instead, it's likely something correlated with S02 in the fit is changing, and so the fitting routine is getting a bit confused and attributing part of the change to S02. (That's not a knock on the fitting routine; it doesn't know any better unless you tell it!)

I think the best recommendation is to do a simultaneous fit on multiple spectra, constraining the S02 to be the same for each. So you're still fitting S02, but forcing all the spectra to use the same value.

Second best is to fit one spectrum and allow S02 to vary, and then constrain all the other fits to use that value.

--Scott Calvin Sarah Lawrence College

On Sep 18, 2014, at 7:06 AM, HOON Kim mailto:science@live.co.kr> wrote:

...

Hello,

I am a bit confused about the amplitude reduction factor (S0^2), in a sense that whether this factor must be determined by fitting or constrained by a reference value for a specific element. I'm dealing with a cathode composite (for lithium-ion battery) comprised of two crystal phases. During charge-discharge, the amplitude reduction factor changes and at a certain state of charge (SOC) it changes a lot such as from 0.77 to 0.67. My understanding is that it may reflect the phase transition of the material into the amplitude reduction factor. But, I'm not sure ... I need advice on this.

Thank you !

Kind Regards, HOON _______

_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

-- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/

This is an excellent point, and I'd like to elaborate yet further. :) How does one tell whether transferability is justified or not, based on the experimental data? Perform fits with the S02 constrained to some reasonable value (perhaps the average of your results). Compare the reduced chi square reported by the fit for the case where S02 was guessed to the one where it was constrained. If the reduced chi square is significantly higher for the constrained case, then transferability is not justified; i.e., the data is fit better, in a statistical sense, when S02's are fit separately for each spectrum. If it's lower or about the same, then transferability is justified. (But keep in mind that an apparent lack of transferability might be due to inconsistent determinations of the edge jumps.) How much higher is "significantly" higher? There's a statistical test called the Hamilton test that can help you decide that, if you really want to be careful about things. But looking at the reduced chi square is a good first step. Note that what I'm saying is closely related to Bruce's other comment about including error bars on the reported values. If the reported ranges including error bars all overlap, it's also likely that you'll find that constraining all the fits to have the same value of S02 will not increase the reduced chi squares significantly. So what if transferability is justified by the data (i.e. compatible with it)? Does that mean you should do it? At that point the decision which to present as the "primary" fit becomes to some extent aesthetic. The statistics are then telling you that the data is consistent with transferability, but of course there may be some "actual" variations due, perhaps, to the cause Bruce suggested. Would you prefer to explain in a paper why you are constraining the S02's to be the same, or why you have different values for them? In either case, if you had performed fits both ways, you could look at the values generated by both sets of fits and see if they were consistent; that is, if the ranges specified by their error bars overlap. If that were the case, you could say so in your paper, and then whether or not you constrained the S02s to be the same becomes mostly a non-issue for readers. And if the ranges didn't overlap, then you should report that too, suggesting that there is some additional uncertainty based on your results based on the question of S02. --Scott Calvin Sarah Lawrence College On Sep 18, 2014, at 9:04 AM, Bruce Ravel wrote:

On 09/18/2014 07:23 AM, Scott Calvin wrote:

...

Hi Hoon,

Using a reference value is not always a good idea, because experimental effects can play a role.

I want to elaborate a bit on this point in Scott's post, particularly given the nature of your sample.

The materials in a battery, as they charge or discharge, can undergo changes in morphology. Morphology can have an impact on the measured amplitude. More specifically, inhomogeneity in the sample -- pinholes, for instance -- have a known effect on the amplitude. See, for example:

http://dx.doi.org/10.1103/PhysRevB.23.3781 http://dx.doi.org/10.1016/0167-5087(83)90730-5 http://gbxafs.iit.edu/training/thickness_effects.pdf

My point is that you may need to question the assumption that S02 even should be transferable in your measurement.

B

...

BUT, S02 should not change during charge-discharge on a single sample, or a series of samples prepared and measured similarly. Instead, it's likely something correlated with S02 in the fit is changing, and so the fitting routine is getting a bit confused and attributing part of the change to S02. (That's not a knock on the fitting routine; it doesn't know any better unless you tell it!)

I think the best recommendation is to do a simultaneous fit on multiple spectra, constraining the S02 to be the same for each. So you're still fitting S02, but forcing all the spectra to use the same value.

Second best is to fit one spectrum and allow S02 to vary, and then constrain all the other fits to use that value.

--Scott Calvin Sarah Lawrence College

On Sep 18, 2014, at 7:06 AM, HOON Kim mailto:science@live.co.kr> wrote:

...

Hello,

I am a bit confused about the amplitude reduction factor (S0^2), in a sense that whether this factor must be determined by fitting or constrained by a reference value for a specific element. I'm dealing with a cathode composite (for lithium-ion battery) comprised of two crystal phases. During charge-discharge, the amplitude reduction factor changes and at a certain state of charge (SOC) it changes a lot such as from 0.77 to 0.67. My understanding is that it may reflect the phase transition of the material into the amplitude reduction factor. But, I'm not sure ... I need advice on this.

Thank you !

Kind Regards, HOON _______

_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

-- Bruce Ravel ------------------------------------ bravel@bnl.gov

National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973

Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit